<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>REM测试</title>
</head>
<style>
  html {
    font-size: 100px;
  }
  .box {
    font-size: 1rem;
  }
  .box1 {
    font-size: 100px;
  }
</style>
<body>
  <div class="box">REM单位1rem</div>
  <div class="box1">REM单位100px</div>
</body>
</html>